All the software and data in a computer are stored on internal storage (hard disk, SSD) as "files," and files are organized into "folders" in a hierarchical structure. A folder simulates an ever-expanding paper folder in a file drawer, and the route to a file is called the "path." The folder hierarchy is visually navigated with the Explorer file manager that comes with Windows. To launch Explorer, right click the Start menu and select File Explorer, Open Windows Explorer or Explore, depending on the Windows version. See Win Explorer
The Primary Drive Is Local Disk C:
The "C:" is a legacy designation. The first personal computers had two floppy drives labeled A: and B:. Thus, when the first hard drive was added, C: was the next letter. Additional data and programs may be stored on external hard or solid state drives (SSDs) that are connected when needed, and they become drives D:, E:, etc.
Windows comes with predefined folders, and applications default to saving data in Documents, Music, Pictures and Videos (WinXP and 7 have a "My" prefix (My Documents, My Music, etc.). However, the exact location of these folders changes with each version of Windows.
Notice the folder hierarchy in the example below. The white, right facing triangles indicate that there are subfolders in the folder, and clicking the triangle makes the next subfolder level visible. When the subfolders are displayed, the triangle turns dark and faces downward.
Windows 7 and 8 Hierarchy
Favorites, Libraries, Computer and Network (blue arrows) are the high-level categories. Note the Desktop and My Documents folders (red arrows) are duplicated, because Favorites and Libraries are pointers to the actual folders under Users.
Windows XP Hierarchy
In Windows XP, My Documents is located at the top under Desktop, but is actually stored under Documents and Settings. Each version of Windows relocates the default folders. For example, Vista changed the name of My Documents to Documents and made it visible in three places in Explorer.